The present invention relates to a method for processing plastic material webs, the webs being provided with card-shaped images separated by a blank grid. Upon completion of the processing, the individual images will be punched from the web thereby producing credit cards, telephone cards, smart cards, and the like. The remaining blank grid is discarded.
Processing of such webs must meet extreme accuracy requirements. For example, when milling a recess into a card body for accommodation of a chip, the site of the recess must not deviate from predetermined coordinates relative to the card edges.
Frequently, such webs or cards are produced as multi layer laminates. In a laminating installation, the layers are hot pressed and then cooled down. A web so produced undergoes a shrinking process, that is, the dimensions of the web in longitudinal and transverse directions decrease. Even if the shrinking of, say, a few tenths of a millimeter amounts to only tenths of a percent when related to the standard card length of 86 millimeter, it nevertheless detrimentally affects the operations in following processing stations. Misalignments and/or distortions of the printed image on the cards may result from shrinking.
In a known plastic card fabrication process, positioning holes are provided in the blank grid for cooperation with positioning pins located at the various processing stations so as to present the to-be-fabricated cards in proper alignment. While the distance reduction due to shrinking may be insufficient to bring immediately succeeding holes off the capturing range of the pins, this may not hold true if the pins are allocated to each second hole or have even greater spacing.
The shrinking problem is aggravated additionally because it is not a fixed parameter but may vary depending upon the used material and may even vary when a fresh batch of one layer is processed.
German published patent application DE 36 12 518 A1 discloses a process wherein a plastic body is produced e.g. by means of injection molding. The body so formed is subjected to a cold deformation so that it may fit on some other member. The body is then heated and tends to assume its originally molded shape. For example, a bottle cap is produced, then widened so that it fits over a bottle mouth, and heated to shrink thereon. It will be appreciated that the problem underlying the teaching of '518 as well as the steps taught to solve it are quite different from the present invention.